Abstract

Heavy mass ions, Kr and Xe, having energies in the ~10 MeV/amu range have been used to produce thick planar optical waveguides at the surface of lithium niobate (LiNbO3). The waveguides have a thickness of 40-50 micrometers, depending on ion energy and fluence, smooth profiles and refractive index jumps up to 0.04 (λ = 633 nm). They propagate ordinary and extraordinary modes with low losses keeping a high nonlinear optical response (SHG) that makes them useful for many applications. Complementary RBS/C data provide consistent values for the partial amorphization and refractive index change at the surface. The proposed method is based on ion-induced damage caused by electronic excitation and essentially differs from the usual implantation technique using light ions (H and He) of MeV energies. It implies the generation of a buried low-index layer (acting as optical barrier), made up of amorphous nanotracks embedded into the crystalline lithium niobate crystal. An effective dielectric medium approach is developed to describe the index profiles of the waveguides. This first test demonstration could be extended to other crystalline materials and could be of great usefulness for mid-infrared applications.

Figures (5)

Electronic energy loss of Kr (809 MeV) and Xe 1432 MeV as a function of penetration depth in LiNbO3 obtained with the SRIM-2003 code [17]. For comparison with earlier experiments [12], the case of Cl (45 MeV) is also shown.

Optical micrographs from the polished edge of 1-mm thick Z-cut LiNbO3 samples irradiated (from left to right) with Xe ions of fluence 2x1011 cm−2 recorded in (a) transmission mode where the absorbing irradiated layer appears darker, (b) dark-field reflexion mode where the irradiated layer appears brighter than the substrate due to scattering centers, and (c) standard bright-field reflexion mode where a faint line at the depth of the end of ion range appears with different contrast.

(a) Track radius vs depth obtained from a calculation using the inelastic thermal spike model developed by Meftah et al. [10] and (b) Theoretical refractive index profiles that would correspond to the track profile shown in (a) for the fluences of 2x1011 and 4x1011 cm−2, calculated according to an effective medium approach as discussed in the text. The index profile optically determined for the same fluences are shown (dashed line).

Tables (1)

Table 1 Irradiation parameters including the electronic energy loss Se at the sample surface and at the Bragg maximum as well as the maximum nuclear energy loss Sn and the projected ion range Rp according to the SRIM-2003 code [19]

Metrics

Table 1

Irradiation parameters including the electronic energy loss Se at the sample surface and at the Bragg maximum as well as the maximum nuclear energy loss Sn and the projected ion range Rp according to the SRIM-2003 code [19]